The present invention relates to a voltage monitoring system and voltage monitoring module and relates in particular to a voltage monitoring system and voltage monitoring module to monitor the voltage of cells in a battery pack utilizing multiple cells coupled in series as one battery cell.
In recent years, battery cells that supply electrical power to the motors such as in automobiles often use battery packs that are multiple cells coupled in series as one battery cell. An equal voltage must be maintained in the cells in order to maintain performance in this battery pack. Numerous voltage monitoring systems have therefore been proposed for monitoring the voltage in each of the battery cells that form the battery pack.
In the voltage monitoring systems, one voltage monitoring module is installed for multiple battery cells, and multiple voltage monitoring modules monitor the voltage of all cells in the battery pack. The voltage monitoring modules operate at this time from power supplied from the battery cell group for monitoring. Therefore, when a difference in electrical current consumption occurs among the voltage monitoring modules in the voltage monitoring system, then a difference in battery cell electrical current consumption speed occurs between a battery cell group monitored by one voltage monitoring module, and the battery cell groups monitored by the other voltage monitoring modules. This difference in electrical current consumption speeds causes a difference in voltage among the battery cells, creating the problem of a drop in battery pack performance.
Japanese Unexamined Patent Application Publication No. 2010-81692 therefore discloses a technology for equalizing the current consumption in multiple voltage monitoring modules. Japanese Unexamined Patent Application Publication No. 2010-81692 is technology relating to a vehicular power supply monitoring device. FIG. 17 shows a block diagram of the vehicular power supply device disclosed in Japanese Unexamined Patent Application Publication No. 2010-81692. The vehicular power supply device shown in FIG. 17 includes a drive battery 101 including multiple battery cells 103 coupled in series to supply electrical power to the motor driving the vehicle; and multiple sensing circuits 105 to isolate the drive battery 101 into multiple cell blocks 102 and detect the state in each of the separate cell blocks 102. Each of these sensing circuits 105 operates from power supplied from each of the cell blocks 102. Moreover, an equalizing circuit 110 for equalizing each of the cell block 102 load currents to a specified current value is coupled to each of the sensing circuits 105. This equalizing circuit 110 equalizes the load current in each of the cell blocks 102 per the operating state of each sensing circuit 105.
FIG. 18 shows a block diagram of the equalizing circuit 110 disclosed in Japanese Unexamined Patent Application Publication No. 2010-81692. The equalizing circuit 110 in FIG. 18 increases or decreases the balance current flowing in the balance current adjusting circuit 113 according to the increase or decrease in the voltage differential occurring across both ends of the current detector resistor 112 according to the electrical current (consumption current) flowing in the current detector resistor 112. More specifically, the balance current adjusting circuit 113 increases or decreases the balance current flowing in the output transistor 117 based on the voltage differential between the reference voltage 115 and the amplified voltage output from the differential amplifier 114 amplifying the voltage differential occurring across both ends of the current detector resistor 112. The balance current at this time lowers if the voltage differential across both ends of the current detector resistor 112 increased, and rises if the voltage differential across both ends of the current detector resistor 112 has decreased. The size of the balance current can be set by varying the reference voltage 115. The current setting adjusting circuit 120 varies the voltage value of the reference voltage 115.
The vehicular power supply device disclosed in Japanese Unexamined Patent Application Publication No. 2010-81692 in other words equalizes the consumption current among the sensing circuits 105 by setting the reference voltage 115 so that the consumption current flowing in each of the sensing circuits 105 is the same or larger than the largest consumption, current among the consumption current flowing among the sensing circuits 105.